The present invention relates to an image reader and a book document reader with a page turning capability which are associated with a copier, facsimile transceiver or similar image forming apparatus for reading a document in the form of a book.
A conventional image reader for a book document has a document table on which a book document is laid spread and face up, a glass platen contacting the spread surface of the document, and scanning optics facing the document with the intermediary of the glass platen for optically scanning it (referred to as Prior Art I hereinafter). Another conventional image reader optically scans, or traces, the surface of the book document held in the above-mentioned position by use of a contact type optical read sensor (referred to as Prior Art II hereinafter). The problem with Prior Art I is that a book document has to be moved from a position for turning the pages to a scanning position, resulting in a low scanning efficiency and a bulky construction. Prior Art II is practicable without resorting to a bulky construction. However, since Prior Art II is not provided with means for pressing the spread surface of a book document, it is likely that the surface of the document rises away from the document table and cannot be stably scanned.
In the light of the above, there has been proposed a device capable of reading a book document while turning over the leaves of the document, i.e., a multifunction document scanner (MFDS), as disclosed in Japanese Patent Application No. 193589/1990 by way of example. The MFDS includes a document table having a document loading surface, a belt extending along the document loading surface while being partly spaced part from it, and a page turning and reading unit. The page turning and reading unit has leaf accommodating means, leaf attracting means, leaf separating means, reading means, etc. After a book document has been set on the document loading surface in a spread position, the page turning and reading unit is moved relative to the surface of the document to read the document while sequentially turning over the leaves of the document. The MFDS, therefore, fully automates the time and labor consuming operation for turning over the leaves as well as the document scanning procedure, thereby remarkably enhancing the productivity of, for example, copies.
The prerequisite with the MFDS is that the size of the book document laid spread on the document table be detected to determine a reading area and a page turning area of the document. To meet this requirement, in the MFDS, the edge of the spread book document is detected by an exclusive sensor or by image processing while the page turning and reading unit is in a prescanning movement. Then, the outputs of an encoder mounted on a turn-over roller are counted to determined the size of the document and thereby the reading area and page turning area.
However, regarding a book document or similar relatively thick document, the edge of the surface of the document changes in position with the change in the thickness of the document, pages at which the document is spread, etc. It is, therefore, preferable to adequately set up the position for starting scanning the document and the position for starting turning over the leaf in matching relation to the actual edge of the document surface, actual image position, etc. Otherwise, the page turning operation would become defective and, in the worst case, errors would be introduced in images to be taken in or printed out.